Find the magnitude of the electric field at a point 0.105 m outside the surface of the sphere.
Take the permittivity of free space to be epsilon_0 = 8.85×10−12 C^2/(N*m^2) The field is the same as if all the charge were a point charge situated at the center of the sphere (and there were no sphere present).
So r = 0.480 + .105 = 0.585 m
Use E= F/q
E=k Q/r^2 =(9 x 10^9)(0.280 x 10^-9C)/ (0.585 m)^2
E= (9 x 0.280) / (0.585^2) = 7.36357659
E= 7.36 N/C